1. Field of Endeavor
The present invention relates to a fuel lance for introducing fuel into a gas flow in a combustor of a gas turbine engine, in particular a gas turbine with sequential combustion.
2. Brief Description of the Related Art
A gas turbine with sequential combustion is known to improve the efficiency of a gas turbine. This is achieved by increasing the turbine inlet temperature. In sequential combustion gas turbine engines fuel is combusted in a first combustor and the hot combustion gases are passed through a first turbine and subsequently supplied to a second combustor, known as an SEV combustor, into which fuel is introduced. The combustion of the hot gases is completed in the SEV combustor and the combustion gases are subsequently supplied to a second turbine.
The emissions regulations for gas turbines are, however, becoming ever more strict and ways are needed to maintain the efficiency of the gas turbine whilst reducing harmful emissions. In order to improve emissions, the processes occurring in the combustion chamber are of critical importance, in particular the mixing of the fuel with the oxidization gases. The conditions in the combustion chamber are particularly important when using hydrogen rich fuels, for example MBTU, which have a lower ignition delay time, higher adiabatic flame temperature and higher flame speed. These properties increase the tendency to produce harmful emissions, for example NOx. These high H2 content fuels also have lower densities compared to conventional fuels such as natural gas, they therefore require a larger flow rate into the combustion chamber. The application of existing combustor designs to such fuels results in high emissions and safety problems. Existing combustor designs have a fuel lance for introducing the fuel into the hot gas flow. The fuel is introduced in either a radial or an axial direction. A problem encountered in these designs, especially with the use of hydrogen rich fuels, but also with more traditional fuels, is an uneven mixing in the 3D space and time resulting in higher emissions. The fuel jets are also orientated in such a way that the H2-rich fuel reaches the burner walls far upstream of the exit of the mixing zone, whereby fuel residing close to the burner wall promotes undesirable auto ignition (i.e., premature ignition). Existing burner designs also do not allow multi-fuel injection without compromising on emissions or flashback safety.
Radially injecting a hydrogen rich fuel, such as MBTU, into an oncoming oxidization stream is problematic due to the blockage effect of the fuel jets (i.e., the stagnation zone upstream of the jet where the oncoming air stagnates), increasing local residence times of the fuel and promoting auto ignition. The shear stresses are highest for a fuel jet perpendicular to the main flow and the resulting turbulence may be high enough to permit upstream propagation of the flame.